I have a strange issue with munin on Ubuntu 16.04. All the graphs are ok but the network traffic and errors which are empty.
I see nothing in the logs about it, and running:
munin-run if_eth0
gives the output:
down.value 5382101121
up.value 79038417951
which seems ok to me. Running if_err_eth0 works too, but the graphs are like this:

How can I fix this strange behaviour?